Acetylation process and product



May 22, 1945. J, D, MURRAY 2,376,378

ACETYLATION PROCESSIAND PRODUCT Filed sept. 2d, 1941 Y f' f /av Moo Patented May 22, 1945 2,376,378 AcETytATioN PROCESS `AND PRODUCT p John D. `Murray, Chicago, Ill. m Application september 20,1941, seria1No.411,745 6 claims. (c1. 260g-234) The` present invention `relates to acetylation products of starch and dextrin and methods of making the same, -and is more particularly concerned with primary, low viscosity acetylation products of starch or dextrin suitable for use in thermoplastic coating compounds.

This application is a continuation-in-part of my copending application Serial No. 296,295, filed September 23, 1939, which in turn was a continuation-in-part of my earlier application Serial No.:V 251,944, filed January 20, 1939.

y To be suitable for ordinary commercial pur! poses, starch, dextrin and other carbohydrate acetates should be readily soluble in commercially available solvents, such for example as acetone.

The `acetylation of carbohydrates is unique in that all `the processes now used, so far as I am aware, first make an acetylation product insoluble inacetone and then hydrolyze back to an acetone soluble acetylation product. This procedure was first described by Miles in 1903 in United StatesPatent No. 838,350`and is the foundation on which the present cellulose acetate industry is built.

In carrying out such prior commercial processes i based on the Miles disclosures, it has been the `practice to dry cotton or cellulose to about 5 per cent moisture content or less and to `react the ingredients in a primary reaction' in the proportions necessary to form triacetate as a final productif In such prior processes, the carbohydrate, such as dry cotton having a moisture content of about 5 per cent, is agitated with glacial acetic acid and is then reacted with acetic anhydride and 7 to 10 per cent of sulfuric acid which acts as a catalytic' f agent. The amount of sulfuric acid added v aries between '7 to 10 per cent by weight of the acetic anhydride utilized depending upon the type of acetate'desired. To avoid charring, the sulfuric acid is diluted with a` considerable quantity of acetic acid and is slowly added to the charge of cotton and glacial acetic acid, and 4agitated to secure uniformity. The acetic anhydride is then slowly added to the mixture to convert the cellulose to the acetate. A cooling system which pro-` i vides close temperaturecontrol is anessential part of the reacting equipment, and the temperature must be closely regulated by use of the cooling system to prevent too rapid a reaction and too `much degradation of the molecule.

The foregoing reactions are usually carried out at temperatures ranging between 40 C.-50 C.

#UNITED STATES PATENT NOFFICE a period of about thirty-six to forty hours. `At this stage the mixture contains mainly cellulose triacetate which is soluble in chloroform, but not in acetone. '1. i

To render the acetates so produced soluble in acetone,the mixture is subjected to afripening and saponication process which involves the hydrolysis of the triacetate back to an acetate having a lower acetic acid. content. Usually the hydrolysisreaction iscarried by addition of water and acetic acid. The temperature of the mixture is maintained at about 40 C.-50 C.(l04. Etf-122 F.) ,during this stage for a period of about twelve to eighteen hours.. i

Cellulose acetate is then precipitated from `the solution of cellulose acetate in acetic acid so produced by adding cold water. The cellulose acetate is then ltered cut,1washed thoroughly and -dried at temperatures between 35 C.-40`C. (95

The cellulose acetates so produced are soluble in acetone and have a combined acetic acid content of from 51 to 58 per cent. The acetates produced by theseV processes are all of low combined acetic `acid. content, and highviscosity and high melting points. For example, the highest combined acetic `acid content claimed for such acetates in any of the prior commercial literature on this subject appears to be from 60 to 62 per cent, and the meltingpoints range from 450 F. to 550 F. Such acetates are not runable below 300 F.

Commercial starch acetate has also been made `by theMles process, or similar variations thereof, and both process andproduct are subject to the above pointed out disadvantages and objections, especially `insofar vas the commercial thermoplastic coating field is concerned. l

Commercially practical` thermoplastic coating composition must have relatively low viscosity and must` be runable at temperatures `ap1c reciably lower than any temperature at which the surface to be coated will be injured. Usually for thermoplastic composition for coating paper, it is required that thisfrunable temperature be less than 300 F. The' prior cellulose and starch acetates have accordingly not been usable for such coating compositions,

The prior processes have also been subject to the following practical disadvantages:

1. They takea great dealfof time. The speediest commercial process of the prior art; which is at present known is generallythat above described and this takes at least forty-eight hours or more to consummate. Y i

2. They are relatively costly due to the fact that acetic anhydride must be used in large excess of the theoretical quantities required for the reactions.

3. Large amounts of II2SO4 or other more expensive catalysts are; used, requiring cooling .to retard the reactions and to prevent degradation.

Accordingly, it is the primary object rof the present invention to provide a novel process for' manufacturing a primary, low viscosity acetylation product ofa material selected from the group of carbohydrates consisting of starch or dextrin,

and the resultant novel acetylation product which` is soluble in acetone and substantially insoluble in water, oils and greases.

. A further object of the invention is to provide novel, economical and speedy methods of manufacturing primary starch or dextrin acetylation products which are soluble in a, ketone. such as acetone. l

A further object of the invention is to provide novel methods for `manufacturing acetone soluble acetylation products of! starch or dextrin which have definite and controlled combined acetic acid content.. Specically, acetone soluble acetylation products' having cOmbinedaCetic. acid contents of from approximately 48 per cent to as high as 75 per cent are produced.

A further object of the invention is to provide novel methods of manufacturing starch or dextrin acetylation products which give. solutions having low viscosities and melting points, and which'are comparatively stable in molten condition, so that they are adaptable for use in thermoplastic coating compositions. i

A further object of the invention is toprovide a novel ymethod of preparing acetylation products of material selected from the group consisting of starch and dextrin wherein the ingredients are rapidly reacted in the presence of "a relatively small quantity of catalyst at a relatively high a novel method ofV acetylating starch or dextrin wherein the reaction4 temperature of the material with an acetylation agent such as acetic4 anhydride is controlled and maintained. at a relatively high level without degradation of the product, by use of a much smaller quantity of catalyst than heretofore used. Preferably the reaction is maintained: between 140 F. and 250V F. usually at about 235 F. to avoid substantial evolution of fumes during the reaction.

A further object of my invention is to provide a novel method of making a coating composition containing an acetylation product of starch or dextrin, wherein acetylation is followed in a substantially continuous operation by novel process steps leading to manufacture of the coating composition and accompanying high recovery of the acetic acid resulting from acetylation.

Further 'objects of the invention will presently MOISTURE CONTENT In carrying out my invention, the initial moisture content of the starch or dextrin utilized is an important factor. The presence of an initial moisture content above approximately seven per cent is desirable to my process. In practicing my invention, starch or dextrin having moisture contents above seven per cent and preferably in the range of 171/2 per cent to 12 per cent is utilized. Other things being equal, I have found that the lowest viscosity and most useful acetylation products are produced when the starch or other substance has an initial moisture content of 'I1/2 per cent or more, and the most economical results are secured with moisture contents in the range of 'I1/2 per cent to 12 per cent within which range the reactions proceed spontaneously using a minimum amount of catalyst and produce the highest grades of acetylation products. A sharp difference in solubility, viscosity and quality of the product results when initialV moisture contents of less than approximately 7 per cent arefused The moisture present in my improved process reacts with acetic anhydride to form aceticacid inproportions beneficial to my improved reactions. If necessary, I wet the carbohydrate to bring the moisture up to the desired point, or'add sucient acetic `acid to makeup for the moisture deficiency.

While the normal moisture content of commercially available starches lies in this' range,

appear as the description proceeds in connection the advantage of using carbohydrates while retaining their normal moisture contents or insuring that they have at least normal moisture content has never been appreciated before my invention, as evidenced by the carefulv predrying of the cellulose to 5 per cent or less moisture content in prior commercial processes 'such as .the Miles process. I consider my recognition of the value of maintaining and insuring moisture contents in the higher limits above specied as one'oft'he important novel features of the invention.

If the carbohydrate used in my process has a' moisture content as low as five per cent, the reaction is too slow as there is insuflicieni;r water present to properly reactwith the anhydride,

with resultant low reaction temperaturesl anjd the necessity for larger quantities vof catalyst. 'Mois-- CATALYsrs The use of sulfuric acid catalyst emphasized in this application because itis commercially'best available and is less expensive and generally more satisfactory to handle than any of the v usual acetylation catalysts which applicant has used. However, the other known esterication catalysts, such for example as zinc chloride, chlorosulfonic acid, sulfuryl chloride, acetyl chloride, phosphoric acid, nitric acid and ammonium chloride,qall of which have an unusually high affinity for water, can be used in the'practice of my invention.

In general these other known esterication catalysts must be used in larger quantities, than sulfuric acid.v For. example, to obtain substantially identical results in the reaction, itisinecessary to use from 11/2 to 1%,V asy muchsulffuryl chloride (SOClz) as sulfuric acid, and about'flve times as much phosphoric acid as sulfuric acid.

Some of these catalysts, for example, zinc'vchloride, produce lower melting point; 'acetylation products than? others, and `the particulai'catlyst tion.

used depends in great measure on the product desired. All these catalysts are commercially known substantial equivalents for esterication reactions, available tothe technician carrying out the invention. e 5

Where the process is carried continuously beyond the acetate formation stage to the manufacture of a coating composition, such as the method of making Liquafilm hereinafter t be described, it is essential that the esterication catalyst be capable `of forming a heat stable insoluble salt or like compound upon introduction 0f a stabilizing or neutralizing agent.fAll of the foregoing acid catalysts have this quality, "which permits removal of the catalyst from the reacted mixture without combination with the ingredients of the coating composition, e e.

e "Within a given moisture content of the starch, dextrin or dextrose, by varying the amount of e sulfuric acid catalyst utilized in my improved process, acetylation products having different characteristics may beobtained. For example, in one example `of acetylation of starch, `using sulfuric acid equal to about 0.15 per cent' by weight of the anhydride, the acetylation product. pro;- duced was a fine white powder of low viscosity, was tasteless and had a melting point between 284 F. and 302 F. By raising thesuliuric acid content to about 0.425 percent of the anhydride, the acetylation product was discolored,"slightly L bitter in taste, and had a melting pointof about 230 F. and a viscosity slightlylower than the acetylation product produced by using the .15 per cent sulfuric acid, Using morethan 1.0 per cent sulfuric acid, the acetylation product becomes discolored and degraded by the action of the sulfuric acid. i

JThus where concentrated sulfuric acid Baum 66 is employed as the catalyst, as apractical matter and for best commercial results I keep the 14,0 sulfuric acid catalyst charge well below .15 per" cent by weight of the total acetic anhydride.

. In general, proper carrying out of the reaction depends both upon the amount of catalyst and the amount of heat applied to the reaction during"L the acetylation stage. The higher the temperature ofthe reaction, the less catalyst need be employed, regardless of what catalyst is used.

' VI use `as a catalyst concentrated sulfuric acid having a specic gravity of Baume 66 in the amount of about 0.048 percent to 1.0 per cent by weight of thetotal acetic' anhydride used in the reac- 65 The high reaction temperatures andcontrolled reaction technique employedin thev process of the invention, wherein the starch or dextrin is blended with catalyzed anhydride in sucha manner as to prevent the high exothermic reaction temper-f 70" lose acetates; and, asa result, my improved acetylation products are not appreciably degraded or discolored in the mannerwhich occurs when the prior processes are attempted to be Icarried out at high temperatures.

The reacted quantities of starch or dextrin and anhydride in my process are carefully measured, based on computed theoretical yield basis. Due to the high exothermic reaction temperatures, care must especially beV taken to use accurately predetermined quantities of sulfuricacid or other catalyst and to carefully control blending of the reacting starch, dextrin or dextrose and anhydride.` Addition of proportionately too much catalyst, or mixing the ingredients at such a rate as to exceed the boiling point of acetic acid in the troduce a measured quantity of a selected starch or `dextrin from a hopper II"into a container or kettle I2 equipped with a suitable'stirrer or other agitating device I3, and heated by a gas-burner I0. This starch or dextrin consisting of allthe starch or dextrin which isto be reacted, is within` the preferred moisture ,content range above pointed out, and is initially wetted by the addition of a substantial quantity of acetic acid. `Such preliminary wetting of the starch or dextrin mass in the kettle with acetic acid makes possible a controlled reaction involvinglarger quantities of starch or dextrin thanwould be possible if` anhydride was added to unwettedstarch orfdextrin.

Practically, I have found this initial wetting to increase capacity of the process i'lvefoldb` Simply wetting the `starch or dextrin with acetic acid does not start a reaction spontane'- ously. Initiation and continuance `of a reaction requires the introduction of` acetic anhydride in the presence of both considerable heat and a suitable catalyst. I have discovered that it is necessary to raise the temperature of the wettedmass to at least F, to enable a reactionto start,

and in commercial practice the temperature of the wetted mass in the kettle is initially raised to 230 to 235 F. to insure aspeedy reaction. The

reaction temperature must be at least F. to

be noticeable.`

After initially heating the wettedv mass, a measuredquantity of catalyzed acetic anhydride is introduced into the kettle through` conduit I4,

all the while stirring the mass with Vdevice I3..

This catalyzed anhydride preferably comprises `all the anhydride calculated as necessary for the reaction and it is bled into the mass at a con- ,trolled` rate for maintaining-the reaction temperature `high (235 F.245 F.) `but always belowthe boiling point of acetic. acid.

Following is an example of actual commercial f batches and procedure employedin carrying out f this `phase of the invention. n

Example I.-'Starch acetylation product One hundred and twenty-three pounds of starch (9% `H2O) were wetted thoroughly with 118 pounds of glacial acetic `acid in a reaction kettle such as'kettle I2. IThe wetted mixture was then heated to about 235 "and 234 pounds of acetic anhydridecatalyzed `with 80.5 grams of 66 Baume sulfuric acid, bled into the kettle at such a rateas to keep the material at a reacting `temperature of approximately betwee`n235 F. and245-li` until completionl of the. reaction. This amount. 0f.s u1uric. acidamounted. to.; approximately .07.6. per.` cent.. by weight l of .theA anhydridetused. inthe. reaction.v

v. The 1 acetylation; productv of, starch.. resulting from Example I is a white powder.` havinge combined acetic.l acid .content-o Yper cent, a melting.pointof. about 31.0? E. tri-32.0 Randa viscosityy of 1.S secondasmeasured by a. l.i4-.finch fallI ot a. 50..gram weightzin` a. 12%,; per centso.- lutionpf.' the 4acetatet in .90 .per cent. of. acetone and: 10. per. cent. of. alcohol` at roomtemperature in a.v torsion: type.l visco'simeter known as the Cenco viscosimeter.. c y y II have discovered, itipossible. to. continuethe process .from thispoint to Ymanufacture the`ther moplastic. coating compositions knowny as .Liq= uaiilm, lwithoutthe..usualV precipitating or. sepa.- rating out of the acetylation product. c

.Imdoing this, theI reacted. mass..from.kettle I2 is,fed-.directly.intowa ..vacuum stilll I5.. by manipulation. of valves` wand. l1.. in. a. connecting. con.- lduit-l 8i. .A suitable. neutralizing ,andv stabilizing substance whichv will` reactwith.` the catalyst .to form a. heatA stable insoluble salt is mixed with thereactedmass, either in. kettle4 121er still.. l5, Where sulfuric g acid is the. catalyst.. the. neutralizerais preferably titanium` dioxide, lime, soda. ash onmagnesium oxide. l Any other substance.` come binable withthe particular catalyst. toirender the-catalyst inert. canbe. used.` In choosing this substance. it. must. be borne. in'v mind. that. the

catalyst. is. to: be rendered inert. withrespect to the. other. fLiquailmingredientsy to 'be'added and theinert saltor other compound. formed fromthecatalystmust-be suiciently. heat stable `.to withstand the acetic acid distillation process described below., c

At this point. theremaining. ingredients nec- .'.essary to make Liqualm are usually put into the. still.. These. remaining. Liqualm..ingredien ts may bethose. disclosed inmy co-pending appli.-

.cation l Serial. No.. 296,294, filed September 23,

1939` or `may be. those.. ingredients.. disclosed in the` table below.- All.. of.. these.` remaining. Liqua nlm. ingredients. are! of course chosen so. that .their vapor points and-boiling.l ranges. are. higher thanV fthose ofvr acetic. acid.

In addition tothe compositions disclosed in SeriaLNO. 296,29.4, `followingI are. the. ingredients of two highly useful, newly developedv thermoplastic coating compositions, the ingredients of which, other thanthe ester, can be added. directly to .thereacted massas above described.

. Liquafilm P-13. is. ofv especialvalue in coating on top of inks, such a .s.pr.inted-` surfaces.; and Liqualm L. D. 30. is4 extremely flexible,` water and. dirt repellent, and resista-nt to. grease:v and food solvents so as to` be usable-for food; wrap-` ping `paper coating.. c,

The. mixture now in. the` still isv .mixed and .heated and vacuumY distilled.- to1 remove acetic acid` therefrom.. Asr the.. temperature of; the mix- .turezisg raised. to abouttzIOP# E., well: above.-. the? 75,.,k

asia-.3128" boilingrpoint of, aceticacid, the mixture is worked by agitator i9 and .vaporized aceti'cacidpa'sses upwardly into.. a4 condenser. 2l,. from which'. the liquid.. acetic acid. condensate ows througl'i'4 clonduit'22 toa collector tank'23. Stilllil' i`s"g` `rc videdwitha vacuum gaugezli and a thermometer we1L25, andis heated. by a gas burner 261' Condenser 2l is cooled by a cold water circulatoryl recovered; and, because ofthe above conditions and technique of the process, this recovered acetic acidis better than 9'9 per cent-pure.` @This recovery of. 99. per cent pure acid is a very. iinportant featurerof the improvedprocess. High grade acetic acid.,(99% pure) is muchfmore exfpensive vthan commercial acetic acid (98.65% pure) and,y since use of'high grade'acid is' pref'- erable inmy process, by reuse ofthe recovered acetic. acid-'the total cost of the Whole proces is lowered appreciably.

' If. desired at leastpart of. the aceticacid. can be distilled. oi'into tank 23" before introduction of. the.A other Lqual'rn ingredients; but" it. should not be. completely removed at. that time. asthe mass remaining inthe kettle would be, too viscous to handle eiiicintlyf .After distillation. off of. as much, acetic acid as can. be effected, I bleed a smallquantity of hotwater into' the bottom of the stinthrough valve 33. Where the ingredients are 'in.-. the proportion of thev above example, I'iind` abolita quart'. of. hot Water. 'suicient "Since the.. tem.- perature of the mixture in the. still `is.''alooutZf/O" the. hot water is.. immediately converted' to steam which collects the remainingfaceti'c acid in the. liquid mixture. Ihis. dilute acetic. acid vapor is. passed through. the condenser, andlthe residual1 acetic acid iscoll'ected seperately from the iirstrecovery intank 3`4, which isfconnected to conduit 22'by .a pipe. 35 controlledbyvalve, 36.

A valve 3T, below pipe 35, is closed when this operation takes place; and Valve 36 is of course closed. and. valve 31.- open when. pureacetio acid is beingcollected in. tankf23. c Main vacuum. line 29.- is connected. to. vtank 3A by a branch` pipel'38 controlled by a-va1ve.39. This recoveredresidual acetic. acidis rabout 98.6 per cent pure. and satisfactory for. usual commercialpurposes, thereby c still; further reducing the expense of the process.

y poured. into. cooling pans. of Vdesired .shape-fior .c cellulose? acetates, although.:generally.` the. recovered vacid in such.-instances is.A `dilutelf..because oihydrolysis of. the ester. involved in. the? saponi.-

cation-...stepi Y While. agis..pererablegtogauront? taefafetie reacted ingredients.

' torsion" type viscosimeter.

forming portion of the process by preheating the starch or `dextrinvvetted with acetic acid and gradually bleeding in al1 of the acetic anhydride,` as above described,` a variation of the process requiring `somewhat more time butwherein little or no initial preheating of the mixture is involved may be employed if desired.

As a firststep in carrying out this variation of my invention, a measured quantity of catalyzed acetic anhydride is placed in thekettle; and then a measured quantity of a selected starch or dextrin, which may be wetted, with acetic acid, is mixed witlr the anhydride, the quantities of both being such `thatthe reaction temperature, after initiation of the: reaction, will notsubstantially exceed the `boiling point of,` the acetic acid in themixture at prevailing atmospheric conditions. When all.of the' starch or dextrin computed necessary for the reaction is placed in the kettle, the

above` initial charge or'anhydride is less than one-half thetotal anhydride used in thereaction. These measured quantities orstarch or idextrin and i anhydride commence to react `spontaneously and are permitted to continue to reactuntil thereaction temperatures commence to ,l drop.

While this reaction is spontaneous, it is slow to start, and I have round it preferable to preheat to about 140 F. to insure rapid and commercially `satisfactory'progress of the reaction. This acetylation `step takes place relatively rapidly, usually in a few` minutes depending onthe quantities ini volved.` l

The next step comprises gradually adding to .thereaction product so formed, asecond meas- `uredquantity of catalyzed aceticanhydride, at such a rate as to again keep the reaction temperaturemrelatively high, preferably closeto, but

not exceeding, the `boiling point ofacetic acid. 4This step is rather critical.

` It can be carried out in as littleas twenty minutes using laboratory proportions `of ingredients,but in commercial quantitiesthe procedure must be slower.` For 39 Baume) representing 0.113 per cent by weight of safe commercial operation two to three hours is desirable in producing large sized batches.

The amount of anhydride added is selected according` to the nature of the acetate desired to be produced. Using the process of the invention the added anhydridecan be computed on approximately thetheoretic yieldbases to produce diacetates, triacetates,` tetra-acetates, etc., as deaired,Y ,and according to the use for which it is intended.` This is not..possible` witlrthe prior -'comrnercial processes,` vsince in all of Ythese the actual yields are `materially less than the theoretic yields `that may be produced from the Specific examples of desirable commercial `practices 'embodyingthis latter phase of my inventionwill now be described. I

The viscosity measurements hereinafter re`` Alter the reaction temperature started to drop,

ture "I liquai'llm directly as describerdabove, or`

the starch acetylation product may be precipitated by addition of cold water, filtered out, washed toremove all traces of the acetic and sulfuric acids, and dried to powder form.`

Example IIL-Ester 20a-starch acclylallca product 326.5 pounds of starch (10% water content) were placed inthe kettle and wetted thoroughly with 107vpounds of 99 percent pure acetic acid. 238.5 pounds of acetic anhydride were i then dumped into the kettle, initiating thefspontaneous exothermic reaction :The second charge lof acetic anhydride comprised 480 pounds; The total anhydride was catalyzed by the addition of 369.3 grams of concentrated sulfuric acid `(66 the anhydride. The temperatures of this reac-` tion were the same as in Example II. In the above four examples, initialwetting of `the starch or dextrosekwith acetic acid enables largequantitiesof starch ordextrose to be reacted inthe kettle without the reaction becoming so violent as to be uncontrollable. This is preferred commercial procedure. i However,U for smaller batches, `it is not necessary to pre-Wet the starch, dextrin, or dextrose and this omission does notv adversely affect the reaction or the product of acetylation. Following are further examples of this phase of the invention wherein the preliminary wetting stepis omitted, representing earlier but operable and usable developments of the invention.

Further examples illustrative `of` the scopefof` I the invention with regard to the available in,-

lferred to arenot absolute but `are relative, and

are indicated -by` the time of fall of a 50 gram` weightthrough 44 inches of `fall using a Cenco 4iyaamalc 11.-Estgcr'21l4f-sarchf acca/latina l wprod'llct` ,1. ocuhundrcdand nypcuriclc cf starch (10% lwater content) werejplaced' in the kettle and wetted `thoroughly with 75 pounds of 99 pure` concentratedacetic acid. One hundred andflfty qpoundsof acetic anhydride were then dumped into 1 thekettle, initiating a `spontaneous exothermic l reaction which reached `a l high `temperature in the range of230.o 240 E.. l

gredients' and their relative `proportions which may be employed inthe process will now be given. In each instance, all ofthe starch and enough (approximately one-half) of the catalyzeduanhydride are initially mixed 'as explained above,

in the initial reaction stage; and then thezremainder of the catalyzedanhydride is gradually added to complete the reaction, also as abovedescribed. Throughout, the reactionsare speeded by maintaining temperatures just belowxthe boiling point of acetic acid. i l

Eaamplc lv.-sla`rch acetylation modaal In commercial practice one hundred and fty pounds of acetic `anhydride catalyzed by the.,

addition of 21A ounces ('.093 per cent by weight) of sulfuricacid, Baume 66, is placed in a 300 gallon glass-lined or other` suitable kettle,

tating device.

equipped with a reilux condenser and an agi- Then 150 pounds of commercial cornstarch having moisture content of 10.81 per cent H2O is added to the agitated anhydride and thoroughly mixed, With normal `room temperatures the reaction starts immediately, and being exothermic the temperatureoimass reaches aptime.

proximately 240 F. to 250 F. in relatively short stage: substantially complete as evidencedbyga-` Slight. drop ingtemperature-of' the mixture, ful'- ther acetylation'can be:.insti'tuted.` This; further acetylation in practice isf preferablyV instituted` when the mass reaches atemperature of about 2351'F; In'this stage about 1F69 pounds of; acetic anhydride catalyzed" by the addition ot 3% ouncesf (.14 per centbyfweight) of 66 Baume sulfuric'4 acid: is gradually bledinto the mixture' atsucha.y ratenasto maintain a reaction tem-- perature ranging approximately yfrom 170 F. tor- 245' and preferably about` 2.359717; TheY feeding of the catalyzed anhydride in'this stage may beaccurately controlled by-automatic ther mally:l controlled feedingl mechanism.

This ,latter quantity of anhydride may be vari-ed someW-hataccording tothe water content of the starch employed. The lower the starch Water content, the less anhydride need be employed.

This'latter stage off reaction .requires abouti an hourfor completion. Its-completion is.;eviislencedI by a` drop in temperature of the mixture which occurs a few minutes' after the catalyzed anhydride hasbeen completely' added;

- They reactedv mixture isnowf allowedV to stand for about half anhourfatA Whichltimef. it isv clear and homogeneous, V and the. temperature has dropped toa point where the. product can be precipitated Without: "substantialtI generation of obnoxious fumes. At .this'stage-the';mixture comprises starohfacetyl'ation productsinsolutionE in aceticacid, from which. the acetylation products 'may be precipitated by combinationooi the mii:w ture with a large volume` (about il*l totY 1)- of; cold Water-L l i I The starch acetylation product; precipitate is filteredv out;l thoroughly: washed.. tof remove all tracesy of'acid,` andfthe dried byf suitablerap paratus. Y

About 22 0=pounds of" stable starch'.` acetylation 'productf in the formi of i al ilne substantiallyrwhitc powder'V isobtained in `the above` process'. This acetylation producthasf a high combined. acetic acid content ofi about 65v percent, is soluble in acetone, and has a melting pointzof.; approx-i'F matelyr2959 F.' to-305'F.,. gives'isolutionsof. low

viscosity; and may-be used to. forin-v clear',l color-- less films-and coatings, ingthe: manner set forth -in myA coqoendinev applicationaSerial vNo; 296,294. r'filed September '23.19391 The Viscosity of` this acetylation product measured. in ai. 1211/21] per. cent solution in'90 per cent acetoneA andjlO perl cent alcohol at roomv temperature in: the: above-de- 'scribed Cenco viscosimeter was about: 0.8- second. vIt is admirably adapted forfusein thermoplastic compositions for coating. paper orsthe like,

The=above'described 'process maya be" completed in about tWoand one-halfihours or :lessdepend ing upon room. temperatures and other. factorsso that the output of' acetone soluble-'commercially usable acetate from aI factory employ- 'ing the processes of' the-inventionis many times meltingv point ofv the'iacetate producedv i'szreduced .by approximately'5'0'-'F.`

Example V.-Sta1'ch' acetylation product Onehundred pounds of corn starch havingga..

moisture 4content of 10 per cent water is combined with a. total Gf.- 22o-'pounds of acetic/'antimafia catalyzedzwithiour ouncesfof.'sul-fLiric-.acidi` This Y Example. Vivstarch acetylation product Six ounces of laundry'fstarch hay-ing a moisture contentV of- 12.5V per-'cent waterz is combined'with a total' of 1-35 ounces of acetic anhydride catalyzedt with 0.14 percent of sulfuric acidi This reaction yields about? 9 ounces of acetone soluble starchvvacetyl'ation product having' a combined acetic acid content of' 62.2 percent;y andi ai melting point ofi 305 17k-325l FL Theviscosity at'r200w F. of a33i/3i percent solution of" this acetate insdimethoxyI ethyl phthalate ('-Methoxl as'v'measured in the Cenco meter' afbove-described is abouti 16:5 seconds. This acetylation product isfuse'd' in; a coating composition-knownin the=tradefasLiqu'a# lm B+6L VExample VIIf.-.S'.tarcll.acetylaticm` product? I SixY ounces i of potato staren. having.- `a moisture content of' 12.5 per cent Wateris combined with a total of 13.5 ounces of Vacetic anhydridecatalyzedlwith 0.14 per' cent' of' sulfuric acid. j This reaction yields about'9 ounces of acetone soluble 'starch acetylation product having acombined acetic. acid content of"55.6` pier` cent and a melting point of 320`"F;335"F2' The viscosityatZOU F2 of a 331/3 percent solution of thisv acetylation product'. in dimethoxy ethyl. phthalate (ll/.Eeth'o'x as measured in theCenco. meter" above-,described is about 17.5 seconds; This acetylation; product is used. in a coatingv composition; known-inthe trade'as LiqualmzB-T. l i

Sixfounces of` tapiocaflour.- having aimoisture content 'of 13.4- per. cent, water iscombinedlfW-ith a` total: of, 13.25 ounces .of acetic, anhydride {catalyzed with 0.15. per cent-,ot sulfuric acidi: This reaction yields about 9. ounces ofjacetonej soluble starch acetylation product; havinge combined acetic..v acid. content of 6113.. per cent andla I nelt- .ing point of 295 F-.310? E. The .Viscolsity'f'atzfill)9 F; ofv a.. S31/spel', cent solutionf..thisfacetyltion product in dimethoXy ethyl phtha1ate.('M thox),

ast measured in the. Cenco meter abovedes'cribed is;4 about 3.5 seconds. This product is usedi'na coating composition known in the ytrade` as ..Liqua lm B.3-.

Example IX.-Sta,rcl1.`lv acetylationI producty Six ounces ofv tapiocaiiour. havinglamoisture .content of 12.5 per cent.v water. is; combined-.with

a total of 13.5 ouncesof acetic anhydride catalyzed With- 0.09`4`per cent otsulfuri'cacidl. This reaction yields about 9ounces of acetone soluble starch. acetylation` productA having. a combined' acetic. acidcQntent of 6115 per` cent and amelting, pointof 290` F.-315" F2 Theyisrcosity at2'00 Eloi a. 33 1A3tper. cent' solution. of this acetylation product in dimethoxy, ethyl phthalate" ('Mjetlox), ash measured in` the Cenco` meter'Labove-descib'ed is about 3.9 seconds.l This acetylation product-is used in'. a coatingV composition: knot/min the tradeas LiqualmBL8 f f i f- 'rcdntple a melting point of approximately 273 F. to 295 F. The viscosity at 200 F. of a 331/3 per cent solution of this acetylation `product in Methox, as measured in the Cenco` viscosimeter above-described, .is about 2.5 seconds. This acetylation product is used in a coating composition known in the trade as Liquaiilm B-9.

The quantities given in the examples above are satisfactory for a moisture content of from 7` per cent to 12 per cent moisture content, but, with less than 7 per cent moisture, the anhydride should vbe decreased 6 pounds for each pound deciency of water and the amount of catalyst should be increased slightly.

The present invention is also applicable to th production ofl primary `acetone soluble acetylation products of low viscosity directly from starch which is bone dry or of very low moisture con- .tent by the addition of moisture directly, or indirectly through the use of acetic acid as explained below. l

It will be noted that while all of the starches given in the foregoing examples react to` form useful` products, the acetylation products produced are not interchangeable, but their propertiesdiffer depending on the starch used. v

The manufacturing procedure followed in the above examples is substantially the same as above-described for the preferred embodiment,

` care Ibeing taken that the reaction temperatures are high enough to proceed rapidly -but held be` low the boiling point of acetic acid.

Example XI.-Dextrin acetylation product In manufacturing a dextrin acetylation product in accordance with my invention suitable for use in a thermoplastic coating composition known by the trade name of Liqualm B-4, ingredients in the following proportions are employed: 6 ounces potato dextrin H2O), 13.25 ounces acetic anhydride, and 0.15 pei1 cent HzSOi.

This reaction is carried out in the manner aisvas'zs fgreater the amount of chloride the lower the melting point. H

` SUMMARY or NOVEL FEArUREs In general, all of theacetylation products of `the present invention give solutions `of relatively low viscosity.` Most of the acetylation products above-described for the acetylation of` starch and yields about 9 ounces of` dextrin acetylation product powder. This acetylation product has a combined acetic acid content of 63.3 per cent and a melting point of 278 F.288 F. A 331/3 per `cent solution of this acetylation product in Methox at 200 F., as measured using the Cenco viscosimeter above described, hasa viscosity of about 2.5 seconds.

ACETYLATION PRODUCTS RESULTING FROM USE or CArALYsrs OTHER THAN SULFURIC ACID Example Kr-Starch. acetylation product Paper or the like.

`produced by the process of the present invention have meltingpoints ranging between 237 F. and 335 F.the starch` acetylation products having 'melting points mainlybetween 245 F. and `335" F'.

The acetylation products produced by the processes` of the invention are moreover high grade clear ,and substantially colorless in iilms and coatings, and substantially insoluble in water, greases and oils,` so that they are especially suitable for thermoplastic coating compositions for The following table illustrates the wide diiference between the properties of applicants commercial products produced in accordance with.

Example IV, and `the only readily available commercial starch acetate that applicant could nd, which is sold as Niacet starch acetate:

. Applicants 1- Stg ace y a lon acetate product Melting point. 350 to 365 290 to 305 Combined acetic 57 65 Viscosity 6. 8 0.8

` The viscosities in the foregoing tabulation were measured in the Cenco viscosimeter above-described and `121/2 per cent solutions of the acequired by the processes to produce primary ace-` tates insoluble in `acetone which then must be hydrolyzed to produce secondary acetone soluble acetates.

Further, the high reaction temperatures employed in the processes of the `present invention enable speedy completion of the reactions without the necessity of using catalysts in such proportions or for such periods as will cause material degradation of the carbohydrate molecules.

A further advantage of the present invention is that the ultimate yield of the acetylation product is that approximateh to the theoretic yield.

Although the acetylation products made according tothe processes of the invention preferably have high combined acetic acid contents,

usually from 60 per cent to 67 per cent, by suitably varying the ingredients and proportions above recited, acetone soluble primary acetylation products having combined acetic acid contents of from 53 per cent to 75 per cent have been produced.

` The terms starch acetylation product and dextrin acetylation product havebeen given to my novel product to distinguish it in name over the substances usually known as starch and dextrin acetates. 'I'hat my product is different from such known starch and dextrin acetates is shown by its different properties and ability to be used in thermoplastic coatings. However, I believe my mroductmay .trulybe .calleda starch or-adextrin acetate, as representing the acetate .-derivedvfrom a higher acetylation Aof starch or dextrin than has previously beenobtainable The. vinvention maybe .embodied inother Spev`ciic forms without rdeparting from thespirit or essential `characterisics .Pthereofl embodiments are therefore .to be considered in f all respects ,as illustrative and notrestrictive, fthe scope of theinvention .being indicated 'by y.the apy:pended claims rather than .by the foregoing description, .and Yalll changes which come withimthe `meaning and .range of equivalency of the claims are therefore intended to `be embraced therein.

AWhat is claimed and desired tobe secured by United 4States Letters Patent is: f

1. The Hmethod .of ,preparing `a primary, acetone soluble, high grade, low viscosity Vacetyla- .tion .product lof a. .material Yselected from the group consisting .of rstarch land dextrin, which. .comprises reacting a v,quantity .of said material .having moisture .content of approximately 7-12 gper cent with .acetic anhydride Withsulfuric acid as a catalyst in the amount of approximately 0.076 per cent to 1.0 per cent by weight of said.

...product in 90 ,per `cent of acetoneand 10 .percent .oialcohol .at `room A.temperatures in atorsion .type viscosimeter. y

3.v An Aacetylation .product of starch substan- .ftially identical y with that eproduced by .the proc- .essoflclaim 1, saidzproduct havingamelting .point between .approximately 273` y11". .and ,335 F., Iand :hav-ing a :viscosity `in the yapproximate -range of .The .present .asie-,eze

0.5 tas-asesoria measured by a-lirlh fall 0f a. 4gram Weiglfii'uii'i a. 121/2 per centsolutiun of the acetylationfproduct; in `rper. -cent-K of'raoetone rand' 10'per cent `of alcoholfat room temperatures, iny a:"torsiontypeviscosimeten 4 An )acetylation Yproduct of starch asubstangtially l.identical with that produced l'by-the proc'- vess of claim l, vsaid producthavingia icombined lacetic acid lcontent zbetween 53 per cent .fand 'I5 per cent anda-melting .point between .approxi- 'mately273 F.fand'335" F., and havinga viscosity *in the :approximate range of 0.5 to vr'4.0'zseconds Ameasured by a 441inch yfall o'f airgramfweight in la '121/2 per Acent solution of the acetylation product in 90 per centoffacetonefand 10 percent of alcohol at roomtemperatures 'in'aztorsiontype viscosimeter.

:5. An acetylation "product of 'starch substantially identicalwith 4that produced by thefprocess of -c'laim` l, said yproduct vhavingI a Ycombined acetic-content between approximately :53 vper cent and '65 per cent and a melting point between 273 F. and 335 F., and having afvisccsityin the'approximate vrange of 0.5 to 430 yseconds'measured by-a 44 inch fall of a `50gram `Weight ina 12,'1/2

perfcentsolutionpf the yacetylation product in i90 per cent of acetone -and 10 per cent of` alcohol .at room temperatures lin -a torsion type viscosimeter.

.6. 'Ihe method of preparing a primary, a,cetone soluble, 'low viscosity, high ygrade 'acetylation product ofn starch, which comprises 'reacting measured quantities of said-starchhaving aimoisture content of approximately '7-12 ypercentzanizl acetic anhydride with sulfuric acid as Vacatalyst in the amount of 50.076 per cent-to v0.15 per'cent by weight of saidanhydride, Whilev maintaining 'thereacticn temperature between .140 F. and the boiling point of acetic acid under reaction 'conaimons. f

JOHN D. 

